For remote vehicle control and/or remote vehicle monitoring, a radio communication apparatus for use on a vehicle is so constructed as to be supplied with electric power from the battery always even while the ignition switch is off. However, the battery may be dead when the ignition switch is off for a long time while the vehicle is parked. An on-vehicle radio communication apparatus that prevents the battery from being dead forces itself to stop operating when a predetermined time has passed after the ignition switch is turned off. Another on-vehicle radio communication apparatus (see, for example, Japanese unexamined patent publication No. 2003-63330) that prevents the battery from being dead includes a power supply ECU, which is interposed between the battery and various ECUs and monitors the current flowing from the battery into the various ECUs. When the current flowing from the battery into the various ECUs reaches a threshold value, the apparatus forcedly stops the power supply from the battery to the various ECUs.
However, the apparatus that forces itself to stop operating when the predetermined time has passed after the ignition switch is turned off forces itself to stop operating when the predetermined time has passed regardless of the operation of the radio circuit, even when the apparatus operates for data communication, a search out of range, and/or the like, which causes the radio circuit to consume a large amount of current, and/or even when the apparatus operates only for waiting and/or the like, which causes the radio circuit to consume a small amount of current. Therefore, it is impossible for the apparatus to stop operating according to the current consumed by the radio circuit. This makes it impossible for the radio circuit to operate properly.
In the apparatus described in Japanese unexamined patent publication No. 2003-63330, the power supply ECU monitors the current flowing from the battery into the various ECUs. This enables the radio circuit to operate properly according to the consumed current. However, a power supply ECU for monitoring the current flowing from the battery into the various ECUs is necessary as hardware. This increases costs and/or manufacturing man-hours.